Cellulosic fibrous structures, such as tissue products, are in almost constant use in daily life. Toilet tissue, paper towels and facial tissue are examples of cellulosic fibrous structures used throughout home and industry.
Many attempts have been made to provide tissue products which are more consumer preferred than the tissue products offered by the competition. One approach to providing consumer preferred tissue products has been to provide a cellulosic fibrous structure having improved bulk and flexibility, as illustrated in U.S. Pat. No. 3,994,771 issued Nov. 30, 1976 to Morgan et al. Improved bulk and flexibility, may also be provided through bilaterally staggered compressed and uncompressed zones, as illustrated in U.S. Pat. No. 4,191,609, issued Mar. 4, 1980 to Trokhan.
Another approach to making tissue products more consumer preferred is to increase the softness of such products. Softness may be enhanced by providing desired surface characteristics, as illustrated in U.S. Pat. No. 4,300,981, issued Nov. 17, 1981 to Carstens. Another approach to increasing the softness of a cellulosic fibrous structure is to provide an emollient on the cellulosic fibrous structure substrate, as illustrated in U.S. Pat. No. 4,481,243, issued Nov. 6, 1984 to Allen and U.S. Pat. No. 4,513,051, issued Apr. 23, 1985 to Lavash.
Another approach to making tissue products more consumer preferred is to advantageously dry the cellulosic fibrous structure to impart greater tensile strength and burst strength to the tissue products. Examples of cellulosic fibrous structure made in this manner are illustrated in U.S. Pat. No. 4,637,859, issued Jan. 20, 1987 to Trokhan. Alternatively, the cellulosic fibrous structure may be made stronger, without utilizing more cellulosic fibers and hence making the tissue product more expensive, by having regions of differing basic weights as illustrated in U.S. Pat. No. 4,514,345, issued Apr. 30, 1985 to Johnson et al.
Within the constraints imposed by the foregoing ways to make cellulosic tissue products more appealing to the consumer, manufacturers have attempted yet another manner to make the cellulosic tissue products have more appeal to the consumer--improving the aesthetic presentation of such products. A number of approaches have been attempted to improve the aesthetic appearance of the tissue product to the consumer.
For example, embossed patterns in cellulosic fibrous structures are very common. In fact, considerable efforts in the prior art have been directed to embossing cellulosic fibrous structures. One well-known embossed pattern, which appears in cellulosic paper towel products marketed by The Procter & Gamble Company and assignee of the present invention, is illustrated in U.S. Pat. No. Des. 239,137 issued Mar. 9, 1976 to Appleman.
Typically, embossing is either performed by an apparatus directed to one of two well known processes, nested embossing or knob to knob embossing. Nested embossing is illustrated in U.S. Pat. No. 3,556,907 issued Jan. 19, 1971 to Nystrand and in U.S. Pat. No. 3,867,225 issued Feb. 18, 1975 to Nystrand. In the nested embossing process, as illustrated by the Nystrand teachings, protrusions and depressions in the embossing rolls are registered and axially synchronously rotated, producing a like pattern of protrusions and depressions in the cellulosic fibrous structures produced thereby.
Knob to knob embossing registers the protrusions of the embossing rolls, as illustrated in U.S. Pat. No. 3,414,459 issued Dec. 3, 1968 to Wells. Knob to knob embossing produces a cellulosic fibrous structure having discrete sites in each of the two piles bonded together.
Variations in these embossing processes have also been attempted. For example, having embossments on a cellulosic fibrous structure with a major axis substantially aligned in the cross machine direction, is illustrated in UK Patent Application GB 2,132,141 A published Jul. 4, 1984 in the name of Bauernfeind.
However, any of the embossing processes known in the prior art imparts a particular aesthetic appearance to the cellulosic fibrous structure at the expense of other properties of the cellulosic fibrous structure desired by the consumer. This expense results in a trade-off between aesthetics and certain other desired properties and aesthetics.
More particularly, embossing disrupts bonds between fibers in the cellulosic fibrous structure. This disruption occurs because the bonds are formed and set upon drying of the embryonic fibrous slurry. After drying, moving selected fibers normal to the plane of the cellulosic fibrous structure breaks the bonds. Breaking the bonds results in a cellulosic fibrous structure having less tensile strength and possibly less softness than existed before embossing. Unfortunately, this trade-off is not consumer preferred because, as discussed above, softness and tensile strength are consumer preferred properties. Thus, a functional, but plain appearing cellulosic fibrous structure can be transmogrified into a less functional, but visually more attractive, cellulosic fibrous structure through embossing.
Another method to impart visible and aesthetically distinguishable patterns to a cellulosic fibrous structure is by printing an ink pattern onto the cellulosic fibrous structure. The ink pattern contrasts in color with the background of the cellulosic fibrous structure, so that the pattern is aesthetically distinguishable from background of the cellulosic fibrous structure and is readily visually detected by the consumer. Ink printing a pattern onto a cellulosic fibrous substrate has the advantage that any variety of sizes, shapes and colors of patterns may be utilized.
However, printing ink patterns onto cellulosic fibrous structures has several drawbacks. The ink represents an additional material cost which must be accounted for in manufacture and is commonly passed on to the consumer. The ink must be qualified for epidermal contact and not present a biological hazard upon disposal. Ink has been known to spill during manufacture, presenting a health hazard to workers.
Furthermore, the machinery necessary to contain the ink is often complex and sophisticated, as illustrated in U.S. Pat. No. 4,581,995, issued Apr. 15, 1986 to Stone and U.S. Pat. No. 4,945,832, issued Aug. 7, 1990 to Odom. Such complex machinery represents a capital investment and must be frequently cleaned and maintained. Cleaning and maintenance leads to downtime and expense in producing the tissue product having an ink printed cellulosic fibrous structure substrate.
Yet another manner in which a visually discernible pattern may be imparted to a cellulosic fibrous structure is by utilizing the forming section of the papermaking machine used to manufacture the cellulosic fibrous structure. For example, the aforementioned Trokhan and Johnson et al. patents disclose cellulosic fibrous structures having varying basis weights in different regions of the cellulosic fibrous structures.
In particular, Johnson et al. discloses a cellulosic fibrous structure having a continuous high basis weight network with discrete low basis weight regions dispersed therein. Conversely, Trokhan discloses a cellulosic fibrous structure having a continuous low basis weight network with discrete high basis weight regions dispersed therein.
The difference in opacity, which is incidental to a difference in basis weight or difference in density of such regions, will often cause a pattern to be visually discernible to the consumer. Thus, an visually discernible pattern can be formed in a cellulosic fibrous structure by adjusting the basis weight of different regions of the cellulosic fibrous structure.
However, such patterns may neither be aesthetically pleasing nor relatively large in scale. Furthermore, the aesthetic discernibility of such patterns may be limited by foreshortening of the cellulosic fibrous structure which occurs during creping.
During creping, it is typical for a doctor blade to scrape the cellulosic fibrous structure from a Yankee drying drum and cause foreshortening of the cellulosic fibrous structure to occur. This foreshortening results in flutter or rugosities normal to the plane of the tissue. The amplitude and frequency of the flutter will differ in various regions of the cellulosic fibrous structure, in a manner visually discernible to the consumer.
If a region of the cellulosic fibrous structure is too large, rather than foreshorten to an aesthetically pleasing pattern, the region may buckle and hang, presenting a limp, low quality appearance to the consumer. This undesirable appearance frequently occurs when trying to make relatively large scale patterns visually discernible in the cellulosic fibrous structure by using the forming section of a papermaking machine.
Also, elevational differences in various regions of the cellulosic fibrous structure are often aesthetically discernible to the consumer. For example, if one region of the cellulosic fibrous structure is raised or lowered within the plane of the cellulosic fibrous structure relative to another region of the cellulosic fibrous structure, highlights and shadows may appear. The highlights and shadows cause different regions of the cellulosic fibrous structure to appear lighter or darker even though the cellulosic fibrous structure is monochromatic. Furthermore, if the elevational differences are significant the regions will be visually discernible to the consumer due to his or her depth perception.
Accordingly, it is an object of this invention to impart visually discernible patterns to a cellulosic fibrous structure, and in particular, relatively large scale visually discernible patterns to a cellulosic fibrous structure. It it also an object of this invention to provide an apparatus for making such a cellulosic fibrous structure.